Process for forming images



cited This invention relates to a process for forming images in 'light-developable, direct-writing, radiation-sensitive elements, and more particularly to a dry process.

' Light-developable, direct-writing photographic materials have been developed for light writing and oscillo graphic recording purposes which does not require liquid processing such as chemical development. Such materials have many advantages in practical use as the inconvenience of liquid processing can be eliminated, and the image can be viewed at a mini-mum of elapsed time after recording.

-.An improved light-developable, direct-writing radiation-sensitive element is described and claimed in assignees Hunt application U.S. Serial No. 852,190 filed Nov. 12, 1959 (U.S. Patent 3,033,682, May 8, 1962), and corresponding Belgian Patent No. 585,486. The direct-writing photographic element described in this application comprises a support, e.g., paper, coated with a colloid-silver halide emulsion having dispersed therethrough light-sensitive silver halide grains which preferably are in the range of from 0.1 to 10 microns in diameter and containing 0.5 to 120 mole percent or more, and preferably to 60 mole percent, of a stannous sa'lt, 0.1 to 20 or more, and preferably 0.5 to 5 mole percent, of a plumbous salt and an excess of bromide ions, all per mole of silver.

The above photographic element is usually exposed to radiation from a xenon tube and/or a high pressure mercury-arc lamp containing a high proportion of ultraviolet radiation for a period ranging from 0.1 to 10,000 microseconds or more. After exposure, the material is light-developed by exposure to daylight or low intensity incandescent or fluorescent light or by the use of photofiood lamps commonly used in photography.

When using fluorescent lights of the type usually used in ordinary oflice lighting "for light-development, the image is easily visible in approximately 0.1 to 15 seconds with development to maximum density in several minutes. Lightdevelopment by means of ph-otoflood lamps can result in a readable image in about one second or less, with only a moderate increase in background density or fog but the paper must be heated to 120 C. or more during this step.

Although the photographic element and method of exposure and processing described above permits rapid access to the images, certain difiiculties arise where it is desired to read the image records in a room with ordinary artificial illumination over an extended period of time, e.g.,.more than a few hours. Under continued exposure to daylight or room lighting, the image density tends to decrease, thus the readability of the image record becomes impaired by the lowering of the ratio of image to background density. As taught by the Hunt application, chemical fixing makes permanent the original image to background density ratio, however, this involves at least one step of the conventional photographic liquid processing. Such light-sensitive elements under prior art methods of processing, have very low gamma and high latitude which makes them impractical for line copy work.

It is therefore an object of this invention to provide an improved process for forming images in direct writing colloid silver halide elements by a completely dry process tts atent u 324M961 Patented Mar, 22, 1966 using light only as the developing means. It is another 01bjerct to form images having controlled sensitometric characteristics in said elements. A further object is to provide such a process of producing images by light alone wherein the background density or fog and gamma can be ac curately controlled in a simple and easy manner. Still further objects will be apparent from the following description of the invention.

The process of the present invention comprises:

(a) pre-exposing uniformly to non-image-forming radiation which is less intense than the photo-developing radiation, absorbed by the silver halide grains, of low intensity wavelength in the range 3000 A. to 4500 A. for a period of about 1 to about 150 seconds, a radiationsensitive, direct-writing colloid-silver halide emulsion layer having an average grain size of 0.1 to 10 microns and containing 0.5 to 120 mole percent of a water-soluble st-annous salt and at least one water-soluble halide taken from the group consisting of lithium, sodium, potassium, calcium, magnesium and ammonium chloride, bromide and iodide in an amount sufficient to provide an excess of halide ions over that necessary initially to precipitate all of the silver as silver halide,

(b) exposing the pre-exposed layer to image-forming radiation containing radiation in the region of sensitivity of the original emulsion layer, e.g., to radiation from a xenon tube and/or a high pressure mercury-arc lamp containing a high proportion of ultraviolet radiation for a period ranging from 0.1 to 10,000 microseconds, and

(c) photodevelopi-ng the exposed layer by subjecting it to actinic light radiations of wavelengths within the range 3000 to 5000 A. of intensity less than the image-forming exposure for a period of at least 1 second.

Any of the ligh-t-develop-able, direct-writing, radiationsen-sitive elements, free from or containing an optical sensitizing dye, described in the patent applications listed above or in assignees U.S. patent applications: Hunt,- Ser. No. 61,840 filed Oct. 11, 1960 U.S. Patent 3,033,678, May 8, 1962, Hunt, Ser. No. 117,805 filed June 19, 1961, now Patent No. 3,189,456, and Hunt, Ser. No. 137,534 filed Sept. 12, 1961, now Patent No. 3,183,088 can be used in the proces of this invention.

The pre-exposure can be of the same intensity as that used during photodevelopment of the latent image-bearing layer. In this case, the background density or fog is not reduced, but toe speed is reduced which provides a higher gamma. This, in turn, reduces flare or halation around the image edges thereby giving image records of improved sharpness. The pre-exposure is preferably of less intensity that that used for photodevelopment.

In general, the intensity of the pre-exposure radiation will range from 1 to of the intensity of the photodevelopment radiation. photodevelopment radiation intensity of 3800 metercandles was used. The pre-exposure was carried out using two l5-watt T-8 white fluorescent tubes and the intensity was varied by the use of neutral density filters. The latent image exposure was by means of a xenon tube discharge flash. Various exposures were made to obtain several points on the conventional sensitometric H&D curve. .Thcsc are expressed in terms of log E on the H&D exposure scale.

The invention will now be illustrated by, but is not intended to be limited to, the following detailed examples.

Example I A gelatino-silver chlorobromide emulsion washed to remove most of the soluble salts from the mixing step and containing 1 mole percent of plumbous nitrate, 10 mole percent of stannous chloride and 64 mole percent excess bromide ions, all based on the silver halide, was

In the following examples a 3 made, coated and dried in the manner described in copending application, Ser. No. 117,805 filed June 19, 1961 now Patent No. 3,189,456, except that the emulsion was not optically sensitized with an optical sensitizing dye as in that example.

The coated element was pre-exposed to two 15-watt T-8 white fluorescent tubes at an intensity of about 380 meter-candles for the tests reported in the following table. The latent image exposure was made by a xenon flash tube and is given in meter-candle seconds in said table. The element was then photodeveloped at an intensity of 3800 meter-candles for 5 minutes to give the reflection densities as shown in the table.

Pre-exposure intensity, 380 meter-candles Latent image flash precxposure times exposure, metercandle-seconds -0 seconds seconds seconds seconds UINN aomom 0. 0 U lit- M le ume:

Pre-cxposure (lamina Image contrast, time, in seconds 30 Di; D'hnoo-Dlh;

Example II Example I was repeated except that the pre-exposure was carried out using 38 meter-candles intensity instead of 380 meter-candles. The results are as follows:

Pro-exposure times to 38 meter-candles ll'l Flash exposure, exp. meter-candle-seeonds 0 seconds 5 seconds 60 seconds 120 seconds Gamma and contrast variations are shown in the following table:

Pre-exposure Gamma Image contrast, time, in seconds Dian-Dis D1,ooor".

It will be seen that pre-exposure of A the intensity of the photodevelopment light as shown by comparing Examples I and His not as eflcctive as pre-exposure of the intensity of the photodevelopment light.

4 Example lIl Example I was repeated except that the pre-exposure step was carried out at 3800 meter-candles intensity, that is at the same intensity as photodevelopment with the results as shown in the following table:

Gamma and contrast variations are shown in the following table:

Pre-exposure Gamma Image contrast, time, in seconds Disc-D13 Dmoo- D m It will be seen that when the pre-exposure light intensity is equal to the photodevelopment light intensity, fog is not decreased. Gamma is increased for short preexposure times due to a reduction in toe speed. In this case, short-pre-exposure times are necessary to maintain adequate top density.

Example IV Example I was repeated except that the pre-exposure step was carried out at a light intensity of 1900 metercandles with the result shown in the following tables.

Preexposurc times to 1,000 meter-candles Flash exposure, mctercandlc-secouds 0 seconds 5 seconds 60 seconds 120 seconds Gamma and contrast variations are as follows:

Pro-exposure Gamma Image contrast, time, in seconds Dino- 13 'hooo-Drm In this case, the preferred pre-exposure time for the chosen light intensity would be in the range of 5 to 60 seconds. In this example it will be seen that fog is not reduced as much as when the pre-cxposurc was carried out with light of 380 foot-candles intensity.

Example V The emulsion of Example I was optically sensitized with 5,5-dimcthyl-3,3,9-triethylbenzosclenazole carbocyanine iodide.

The emulsion was coated, dried and tested in the manner described in Example I with the following results:

Pro-exposure times to 380 meter-candles Flash exposure.

meter-eandlc-seconds seconds seconds 60 seconds 120 seconds 0. 38 0. 33 0.32 0. 28 0. 43 0. 37 0. Bl 0. 28 0. 5i 0. 50 0. 38 O. 38 0. 58 0. 60 0. 55 0. 5;: 0. 02 0. 50 0. 62 0. 58

Gamma and contrast variations were as follows:

1 5 Pro-exposure (ramma Image contrast, time, in seconds Dian-Dis moo-Dr":

0 .07 0. 24 g 10 0. 26 (i l7 0. 30 120 17 o. 30 0 It will be seen that gamma and contrast was improved by preexposure of optically sensitized elements in the same manner as the non-optically sensitized elements.

Example VI Example V was repeated except that the pre-exposure step was carried out at 38 meter-candles intensity with the following results:

As in the case of non-optically sensitized materials, preexposure of 1/100 the intensity of the photodevelopment light is not as effective as pre-exposure of 1/10 of the photodevelopment radiation intensity.

It will be seen from the above examples and the process is capable of many variations depending upon the utilization of the direct writing material. Although there is a decrease in photographic speed because of the preexposure step, there is a substantial increase in gamma and contrast when the pre-exposure radiation intensity is kept within from 1 to 30% of the photodevelopment radiation intensity. About 10% of the photodevelopment intensity is near the optimum for the pre-exposure intensity.

The pre-exposure step of the present invention may be carried out continuously by passing the paper or film bearing the direct writing emulsion past an exposure station which may be a lamp or bank of lamps capable of provid ing a light flux of suitable intensity at a rate designed to give the desired exposure. Optionally, the exposure may be applied by the manufacturer or the user, and in the latter case appropriate pro-exposure means may be incorporated as an intergal part of equipment for impressing a latent image which may also incorporate means for photodevelopmcnt with or without the use of added heat.

The direct writing products treated according to the present invention exhibit increased image sharpness and usually lower fog. This is advantageous in line and office copy applications where maximum shaprness as resolving power is sought. For example, in copying line drawings, improved resolution obtainable with this process makes it possible to separate closely spaced lines, etc. In addition, the ability to adjust gamma by alteration of preexposure intensity and time makes is possible to obtain a variety of different contrast effects, i.e., variable gamma from a single emulsion. The reduction in fog is particularly desirable when using such materials in the preparation of proof-prints from portrait negatives, etc. The invention is especially advantageous where images are formed in optical oscillographs using low writing speeds.

I claim:

1. A process which comprises:

(a) pre-exposing uniformly to non-image-forming radiation, absorbed by the silver halide grains, of low intensity of wavelength in the range 3000 A. to 4500 A. for a period of about 1 to about 150 seconds, a radiation-sensitive, direct writing, colloid-silver halide emulsion layer having an average grain size of 0.1 to 10 microns and containing 0.5 to mole percent of water-soluble stannous salt and at least one water soluble halide taken from the group consisting of lithium, sodium, potassium, calcium, magnesium and ammonium chloride, bromide and iodide in an amount sufiicient to provide an excess of halide ions over the necessary initially precipitate all of the silver as silver halide;

(b) exposing the pre-exposed layer to image-forming radiation containing a high proportion of ultraviolet radiation and embodying radiation in the region of sensitivity of the original emulsion layer for a period ranging from 0.1 to 10,000 microseconds; and

(c) photodeveloping the exposed layer by subjecting it to actinic light radiations of wavelengths within the range 3000 A. to 5000 A. of intensity less than the image-forming exposure for a period of at least 1 second.

2. A process according to claim 1 wherein the emulsion layer is a gelatino-silver halide emulsion layer.

3. A process according to claim 1 wherein the emulsion layer is on a flexible paper support.

References Cited by the Examiner UNITED STATES PATENTS NORMAN G. TORCHIN, Primary Examiner. 

1. A PROCESS WHICH COMPRISES: (A) PRE-EXPOSING UNIFORMLY TO NON-IMAGE FORMING RADIATION, ABSORBED BY THE SILVER HALIDE GRAINS, OF LOW INTENSITY OF WAVELENGTH IN THE RANGE 3000 A. TO 4500 A. FOR A PERIOD OF ABOUT 1 TO ABOUT 150 SECONDS, A RADIATION-SENSITIVE, DIRECT WRITING, COLLOID-SILVER HALIDE EMULSION LAYER HAVING AN AVERAGE GRAIN SIZE OF 0.1 TO 10 MICRONS AND CONTAINING 0.5 TO 120 MOLE PERCENT OF WATER-SOLUBLE STANNOUS SALT AND AT LEAST ONE WATER-SOLUBLE HALIDE TAKEN FROM THE GROUP CONSISTING OF LITHIUM, SODIUM, POTASSIUM, CALCIUM, MAGNESIUM AND AMMONIUM CHLORIDE, BROMIDE AND IODIDE IN AN AMOUNT SUFFICIENT TO PROVIDE AN EXCESS OF HALIDE IONS OVER THE NECESSARY INITIALLY PRECIPITATE ALL OF THE SILVER AS SILVER HALIDE; (B) EXPOSING THE PRE-EXPOSED LAYER TO IMAGE-FORMING RADIATION CONTAINING A HIGH PROPORTION OF ULTRAVIOLET RADIATION AND EMBODYING RADICATION IN THE REGION OF SENSITIVITY OF THE ORIGINAL EMULSION LAYER FOR A PERIOD RANGING FROM 0.1 TO 10,000 MICROSECONDS; AND (C) PHOTODEVELOPING THE EXPOSED LAYER BY SUBJECTING IT TO ACTINIC LIGHT RADIATIONS OF WAVELENGTHS WITHIN THE RANGE 3000 A. TO 5000 A. OF INTENSITY LESS THAN THE IMAGE-FORMING EXPOSURE FOR A PERIO OF AT LEAST 1 SECOND. 